This study was to elucidate the effects of Ukgan-san on the hyperthyroidism induced by sodium levothyroxine. Hyperthyroidisms were induced by continuous subcutaneous treatment of LT4, 0.3 mg/kg, once a day for 27days, and 1,500, 1,000 and 500 mg/kg of Ulkansan extracts were orally administered, once a day for 15 days from 12th LT4 treatment, and the changes on the body, thyroid gland, liver and epididymal fat pad weights, serum triiodothyronine(T3), thyroxine(T4), thyroid-stimulating hormone(TSH), asparte aminotransferase (AST) and alanine aminotransferase (ALT) concentrations, hepatic lipid peroxidation(LPO), glutathione(GSH), superoxide dismutase(SOD) and catalase(CAT) activities were investigated with throid gland, liver and epididymal fat pad histopathological changes. The effects of Ukan-san extracts were compared with that of propyl thiouracil(PTU), a standard antithyroidic drug 10 mg/kg(intraperitoneally). 1,500 and 1,000 mg/kg of Ukan-san extracts reversed all LT4-induced hyperthyroidisms and these effects indicating their potential in the regulation of hyperthyroidism. Further, the Ukan-san extract normalized LT4-induced liver oxidative stresses, and also reduced liver damages and epididymal fat pad reducements suggesting its antioxidative and relative organ protective nature. However, nor favorable effects on LT4-induced hyperthyroidisms were detected in Ulkansan 500 mg/kg treated rats as compared with LT4 control rats in the present study. These effects of Ukan-san may help improvement of hyperthyroidisms and accompanied various organ damages.